Multi-phase electrical equipment such as generator control units, bus power control units, converters, generators and like equipment require undervoltage detection circuits for detecting when the output voltage of a particular phase is below a predetermined set point. Since equipment of the type described operates over a wide frequency range, the undervoltage detection circuit must operate independent of frequency. Additionally, when the equipment is used on aircraft, accuracy and simplicity are distinct advantages.
Prior to the present invention, such undervoltage detection circuits have been designed using an array of discrete components or several integrated circuits. Operationally these circuits have used capacitors to hold a rectified multi-phase output and to compare the voltage level of a particular phase to a preset reference. Circuits of this type, while accurate, have relatively poor temperature stability, which precludes their use in many applications. Other prior art circuits utilize an RMS to DC integrated chip for each of the phases for converting the individual phases from a sinusoidal signal to a DC signal, and comparing the DC signal to a preset reference. Circuits of this type are relatively expensive to implement.
Accordingly, it is the object of the present invention to provide a multi-phase undervoltage detection circuit which operates accurately over a wide frequency range and has the advantages of accuracy, simplicity and low implementation costs.